PRAGUE – Rates of three common malignancies – breast cancer, prostate cancer, and colorectal cancer – appear to be lower in psoriasis patients than in the general population of the Canadian maritime provinces of Newfoundland and Labrador, a study has shown.
In addition, only a single case of lymphoma occurred in 3,289 psoriasis patients followed for an average of 10 years, Dr. Wayne Gulliver said in presenting preliminary results of the ongoing study at the annual congress of the European Academy of Dermatology and Venereology.
Dr. Wayne Gulliver
The issue of a possible elevated risk of lymphoma in psoriasis patients has been controversial. Findings have been inconsistent. Some studies have reported a significantly increased risk. Among these, notably, was a population-based cohort study of more than 153,000 psoriasis patients and close to 800,000 controls in the U.K. General Practice Research Database. Investigators found an age- and sex-adjusted 35% increased risk of lymphoma in the group with psoriasis (J. Invest. Dermatol. 2006;126:2194-201).
However, lymphoma is an uncommon disease and a 35% increased risk is, from an epidemiologic perspective, only modest. Some studies have not found a significant association between psoriasis and lymphoma. The Canadian maritime study can be added to their ranks, according to Dr. Gulliver, professor of medicine and chairman of the division of dermatology at Memorial University of Newfoundland, St. John’s.
He matched records from a comprehensive research database of psoriasis patients in Newfoundland and Labrador for 1989-2010 with Canadian national and provincial cancer statistics. The purpose of the study was straightforward: "Our patients want to know if their psoriasis affects their risk of cancer, especially with the treatments we’re offering them these days," Dr. Gulliver said.
There were 232 cancer cases in 3,289 psoriasis patients, for a cumulative incidence rate of 588/100,000 population with psoriasis. Although the psoriasis population was divided nearly equally between men and women, 145 men developed cancer compared with 87 women.
Cancer rates were similar regardless of whether patients had mild psoriasis – meaning they received no systemic therapies – or moderate to severe psoriasis.
The cumulative incidence rate of breast cancer among psoriasis patients was 52/100,000 patients with mild psoriasis and 64/100,000 with moderate to severe disease compared with 96/100,000 in the general Canadian population and 84/100,000 among residents of Newfoundland and Labrador. The prostate cancer rate was 103/100,000 patients with mild psoriasis and 75/100,000 with moderate to severe psoriasis as opposed to 121/100,000 nationwide and 129/100,000 men in the general population of the two maritime provinces. The cumulative incidence rate for colorectal cancer followed the same pattern: lower in the psoriasis patients than in the general population.
Nonmelanoma skin cancer rates were relatively high: 142/100,000 patients with mild psoriasis and 122/100,000 with moderate to severe disease. That’s consistent with findings from other studies. It comes as no surprise given the common use of UV therapy and sunlight exposure in psoriasis patients.
Dr. Gulliver noted the relatively small number of cancers to date is a significant study limitation. But that number will grow as the psoriasis patients age; plus, more psoriasis patients are being added to the provincial database. He added that the database provides fertile ground for planned future studies. He said he plans soon to compare cancer rates in psoriasis patients on immunosuppressive therapy with biologic agents or cyclosporine to rates in patients on other agents.
One audience member observed that it seems more than coincidental that increased rates of breast, prostate, and colorectal cancers in the general population have previously been linked to low vitamin D levels. Perhaps the same factor that drives the increase in nonmelanoma skin cancer in psoriasis patients – that is, UV exposure – is responsible for their lower risks of those three common internal malignancies through a mechanism involving enhanced serum vitamin D levels, he speculated.
Dr. Gulliver called that a fascinating hypothesis and one he is now eager to investigate, since he has access to blood samples for the study population.
The study was free of commercial involvement, and the presenter reported having no relevant financial conflicts.